1. Field of the Invention
The present invention relates to a mirror rotating apparatus.
2. Description of the Related Art
A polygon mirror is often used as a laser scanning component in a printer, a digital copy machine, or the like. JP-A 10-325937 discloses a polygon mirror including a triangular top surface and three mirror surfaces around the top surface, and a polygon mirror including a quadrilateral top surface and four mirror surfaces around the top surface. In each of these polygon mirrors, an inclination angle of each mirror surface, i.e., an angle defined between the mirror surface and the top surface, is different. A technique described in JP-A 10-325937 prevents a runout of the polygon mirror by adding an additional partial shape to the polygon mirror when producing the polygon mirror by an injection molding process so as to reduce the degree of eccentricity of the center of gravity of the polygon mirror with respect to an axis of a rotating shaft of the polygon mirror. Meanwhile, JP-A 2002-218721 discloses a technique of adding cuts to a rotor housing for a light deflector to achieve balance correction. The balance correction of the light deflector leads to reductions in vibrations and noise which occur while the light deflector is rotating at a high speed.
Meanwhile, in a scanner motor for use in a video tape recorder as described in JP-A 5-49225, an outer circumferential portion of a rotor yoke includes a flange portion arranged to project radially outward. The flange portion is made of a transparent material, and a large number of detected portions in a color which easily reflects light are arranged on a lower surface of the flange portion by a printing process. In the scanner motor for use in the video tape recorder, a light emitting element included in a reflective photoreflector is arranged to emit light to the detected portions, and a light receiving element is arranged to receive the light reflected from the detected portions, so that a rotational position signal of the motor is generated. In addition, a rotational position of a motor may be detected by a magnet provided in a rotating portion and a magnetic sensor provided in a stationary portion.
In a case where the detected portions are provided by the printing process in a mirror rotating apparatus arranged to rotate a mirror portion including a plurality of mirror surfaces as in the case of the scanner motor described in JP-A 5-49225, an apparatus for performing the printing process and a step of performing the printing process are needed. This leads to an increase in a production cost of the mirror rotating apparatus. Meanwhile, in a case where the rotational position of the motor is detected by using the magnet, the magnet needs to be additionally prepared, and a step of fixing the magnet to the mirror portion is needed. Moreover, as a result of the magnet being fixed to the mirror portion, the center of gravity of the mirror portion may become displaced from a rotation axis, resulting in an increase in runout.